The present invention relates to a process for preparing novel, monodisperse anion exchangers, and also to their use.
U.S. Pat. No. 4,444,961 discloses, inter alia, a process for preparing monodisperse anion exchangers. Here, haloalkylated polymers are reacted with alkylamine.
EP-A 46,535 describes, with reference to U.S. Pat. No. 3,989,650, the preparation of a macroporous strongly basic anion exchanger with uniform particle size by a direct spraying and microencapsulation process. Here, the bead polymer is reacted with N-acetoxymethylphthalimide and subjected to further reaction steps to give a strongly basic anion exchanger having trimethylammonium groups.
The process described in EP-A 46,535 has various disadvantages.
a) First, it pollutes the environment and wastes resources, since the reaction inevitably releases acetic acid, which pollutes waste water and prevents economic operation of the overall process. In addition, account must be taken of the fact that acetic acid residues remain in the product and contaminate it. Residues of the acetic acid may moreover be released from the anion exchanger into liquids which are actually being passed through the anion exchanger for purification.b) The yield of final anion exchanger product in liters per unit of starting material used is insufficient and not capable of further significant increase.c) The utilizable capacity of the anion exchanger (i.e., its capacity to absorb anions) is moreover not sufficiently high.
The object of the present invention was to provide a method for preparing monodisperse anion exchangers, preferably monodisperse macroporous anion exchangers, with high mechanical and osmotic stability of the beads, with an increased absorption capacity for anions, and at the same time with reduced use of resources for preparing the anion exchangers themselves, and with high preparation yield and high purity of the functional basic groups. The products are also free from post-crosslinking.